Usage Examples of "Neural Circuit" and Related Terms
Topic This article lists and discusses examples of how terms like "neural circuit" are used, both in the popular press and also in neuroscience and other scientific publications. Terms like "neural circuit" include, e.g., "neural circuitry", "neuronal circuit", "cortical circuit", "brain circuit", "circuitry in the brain", etc. For greater completeness, this article also lists examples of neuroscience publications that avoid using the term "neural circuit". These publications might, for example, use alternative terms such as "neuronal path", "neural pathway", "brain wiring", etc. Caveat: This article is by no means an exhaustive list of all usage examples of terms like "neural circuit"--many others could be found and listed. Popular Press Items Using the Term "Neural Circuit" or Related Terms (in chronological order) Macknik, S.L., and Martinez-Conde, S., "Mind-warping Visions: 10 Brain Twisters Compete to be the Best Illusion of 2011", Scientific American Mind, January/February 2012, pp. 46-51: *Page 47: "Illusions also offer a window into how our neural circuits create our first-person experience of the world." Grady, D., "How to Teach An Old Brain New Tricks", The New York Times, March 8, 2012, pp. F1, F6: *Page F1: Quoting Arthur Toga, a professor of neurology and director of the laboratory of neuroimaging at the University of California, Los Angeles about what happens when two people have a conversation: "You're changing the circuitry in your brain. That is because you have changed something in your brain to retain that memory." Castro, J., "Sleep's Secret Repairs", Scientific American Mind, May/June 2012, pp. 42-45, discusses a provocative new theory about the purpose of sleep, proposed by neuroscientist Giulio Tononi, University of Wisconsin-Madison: *At pages 42 and 44, Castro describes how Tononi surmised that the "neural circuits" buttressing recently formed memories can be fortified a certain number of times, but then they reach their maximum strength. *At page 44, we learn that electric current flowing through synapses creates the slow-wave signal recorded with electrodes on the scalp. *At page 45, we further learn about neurons constantly chattering with one another through small electric currents shuttling through synapses--the more current flowing, the stronger the synapse. Also, the caption of a figure on page 45 clarifies that an axon is a neuron's main conduit for incoming information. *Caveat: The second and third items above illustrate how far some go in thinking of neurons as being connected in circuits. These views might, however, be inaccurate: Present-day theory generally holds that neurotransmitter, not electric current, flows across the cleft of a synapse, and that most neurons receive incoming information primarily through synapses on their dendrites and somata, and only secondarily through synapses on their axons. Koch, C., "Searching for the Memory", Scientific American Mind, July/August 2012, pp. 22-23, argues that percepts and memories arise in networks of neurons connected by synapses, and describes experiments in which triggering certain neurons in a mouse's hippocampus' dentate gyrus, i.e. neurons that had been activated in a dangerous environment B, can cause a freezing reaction even in a non-dangerous, neutral environment A. *At page 23, Koch summarizes: "Neural circuits in the dentate gyrus of the hippocampus wired up to express an aversive event that happened at B are sufficient to evoke the associated aversive memory, even though the subjects never had experienced anything bad in A." Looking forward, Koch points out: "Whether these circuits are also necessary for this memory, that is, whether deleting these neurons will remove the memory--shades of Eternal Sunshine of the Spotless Mind--remains to be determined (soon)." Jabr, F., "The Connectome Debate: Is Mapping the Mind of a Worm Worth It?", www.scientificamerican.com, October 2, 2012, pp. 1-3, discusses efforts that have produced a wiring diagram, i.e. a complete connectome, of all 302 neurons in the Caenorhabditis elegans nervous system. *Page 2 describes how Martin Chalfie used the C. elegans wiring diagram to identify specific neural circuits responsible for the worm's tendency to wriggle backward when poked on the head and to squirm forward when touched on the tail. *After discussing addition of synaptic weights to connectomes, page 3 argues that, "to understand how neural circuits work, one also needs to know whether the relevant neurons are excitatory--increasing the likelihood that linked cells fire--or inhibitory, muffling their partners instead." *Page 3 also discusses how a static connectome does not capture dynamics of living neural networks: For example, the stomatogastric ganglion (STG) is a pair of neural circuits in crustaceans that generate rhythmic behavior in response to food; one subcircuit repeatedly constricts and dilates the pyloric region of the stomach, and another subcircuit pulsates the gastric mill. Mapping all the connections between the 30 neurons in STG was important but not sufficient to understand how STG controls crustacean digestive systems. For example, in presence of certain neuromodulators, a neuron that contributes to the pyloric subcircuit might instead join the gastric mill subcircuit. Neuroscience Publications Using the Term "Neural Circuit" or Related Terms Purves et al. The following textbooks by Purves et al. provide excellent explications of the term "neural circuit" and use the term in a variety of contexts, some examples of which are as follows: Purves, D., Augustine, G.J., Fitzpatrick, D., Hall, W.C., LaMantia, A.-S., McNamara, J.O., and White, L.E., Eds., Neuroscience, Fourth Edition, Sunderland, Mass.: Sinauer Associates, 2008: *At pages 11-13 (pages 10-13 in Fifth Edition cited below), a section headed "Neural Circuits" explains that, rather than functioning in isolation, neurons in ensembles process information, providing the basis of sensation, perception, and behavior. *Chapter 23, "Construction of Neural Circuits", pages 577-609 (pages 507-536 in Fifth Edition cited below), describes roles of cytoskeleton in constructing neural circuits, including axon growth cone motility and synapse formation. Purves, D., Augustine, G.J., Fitzpatrick, D., Hall, W.C., LaMantia, A.-S., and White, L.E., Eds., Neuroscience, Fifth Edition, Sunderland, Mass.: Sinauer Associates, 2012 is very similar to the Fourth Edition as suggested above, and includes one chapter title changed to include "Neural Circuits": *Chapter 24, "Modification of Neural Circuits as a Result of Experience", pages 537-557. *A section headed "Neural Circuits Governing Sleep", at pages 637-641, is of particular interest because Box 28D embedded at pages 638-639 is titled "Consciousness", but does not relate explicitly to neural circuits involved in consciousness. Other Examples (in alphabetical order by first author's last name) The following publications provide various other examples of how terms like "neural circuit" are used in the field of neuroscience: Anderson, M.L., "Neural reuse: A fundamental organizational principle of the brain", Behavioral and Brain Sciences, Vol. 33, Issue 4, August 2010, pp. 245-313: *Page 245 describes reuse of neural circuitry for various cognitive purposes to be a central organizational principle, and also mentions that circuits can continue to acquire new uses after an initial or original function is established. *Page 246 suggests that "low-level neural circuits are used and reused for various purposes in different cognitive and task domains". Byrne, J.H., and Roberts, J.L., Eds., From Molecules to Networks: An Introduction to Cellular and Molecular Neuroscience, 2d Ed., Burlington, Mass.: Elsevier/Academic Press, 2009: *Hof, P.R., Nimchinsky, E.A., Kidd, G., Claudio, L., and Trapp, B.D., "Cellular Components of Nervous Tissue", Chapter 1, pp. 1-17, at page 1, explain that neurons form circuits constituting the structural basis for brain function, and distinguish macrocircuits that project between brain regions from microcircuits with local cell-cell interactions in a region. *Dienel, G.A., "Energy Metabolism in the Brain", Chapter 3, pp. 49-110, at page 49, explains that changes in activities of neural circuits and networks involved in specific functions govern demand for energy at a local level. *Byrne, J.H., and Shepherd, G.M., "Complex Information Processing in Dendrites", Chapter 17, pp. 489-511, offer an approach that relates electrical current in dendrites to information processing in neural circuits; for example, page 489 defines "microcircuits" as "a specific pattern of interactions performing a specific functional operation"; page 490 proposes that dendrites do whatever is required to process information within their neuron or neuronal circuit, adding the tantalizing point that some dendrites process information without an axon. *Knierim, J.J., "Information Processing in Neural Networks", Chapter 18, pp. 513-537, begins at page 513 by arguing that understanding how neural circuits support brain and nervous system functions is a primary goal of systems, behavioral, and cognitive neuroscience. At page 515, Fig. 18.2 illustrates a simple neural circuit, the stretch reflex. At pages 524-527, a section headed "Iconic Neural Circuits" describes and illustrates a variety of neural circuits that are building blocks of complex neural networks. Page 527 discusses the plasticity of neural circuits. At pages 528-535, a section headed "Example Circuits" describes and illustrates a number of real neural circuits, ranging from relatively simple to complex. *Byrne, J.H., LaBar, K.S., LeDoux, J.E., Schafe, G.E., Sweatt, J.D., and Thompson, R.F., "Learning and Memory: Basic Mechanisms", Chapter 19, pp. 539-608, describe several specific neural circuits: Pages 561-575 describe neural circuits in Aplysia and other invertebrates; pages 575-595 relate to vertebrates. Chao, D.L., Ma, L., and Shen, K., "Transient cell-cell interactions in neural circuit formation", Nature Reviews Neuroscience, Vol. 10, No. 4, April 2009, pp. 262-271, describe how transient cell-cell interactions organize neural connections. Cline, H., "Dendrite Development, Synapse Formation and Elimination", in Squire, L., Ed.-in-Chief, Encyclopedia of Neuroscience, Elsevier, 2009, pp. 427-430, page 430, expresses the hope "that brain activity will increase synapse formation as well as the establishment and maintenance of optimal neuronal circuits." Conway, B.R., Chatterjee, S., Field, G.D., Horwitz, G.D., Johnson, E.N., Koida, K., and Mancuso, K., "Advances in Color Science: From Retina to Behavior", The Journal of Neuroscience, Vol. 30, No. 45, 10 November 2010, pp. 14955-14963, in the abstract on page 14955, describes color as "a premier model system for understanding how information is processed by neural circuits" and, at page 14957, asks whether midget cells form building blocks for "the 'red-green' color-vision circuit" and discusses brain circuitry for both normal dichromatic and normal trichromatic color vision. Jacobs, G.H., Williams, G.A., Cahill, H., and Nathans, J., "Emergence of Novel Color Vision in Mice Engineered to Express a Human Cone Photopigment", Science, Vol. 315, No. 5819, March 2007, pp. 1723-1725: *Page 1723 argues that color vision requires both multiple photopigments and appropriate neural wiring. *Page 1725 proposes that neural circuitry emerged for comparing new and existing sensory responses. Katz, P.S., Calin-Jageman, R., Dhawan, A., Frederick, C., Guo, S., Dissanayaka, R., Hiremath, N., Ma, W., Shen, X., Wang, H.C., Yang, H., Prasad, S., Sunderraman, R., and Zhu, Y., "NeuronBank: a tool for cataloging neuronal circuitry", Frontiers in Systems Neuroscience, Vol. 4, Article 9, April 2010, pp. 1-13, describe NeuronBank.org, a web-based tool for cataloging, searching, and analyzing neuronal circuitry within and across species. Users can search within a species' brank or perform queries across branches to look for similarities in neuronal circuits across species. Nicholls, J.G., Martin, A.R., Fuchs, P.A., Brown, D.A., Diamond, M.E., and Weisblat, D.A., From Neuron to Brain, Fifth Edition, Sunderland, Mass.: Sinauer Associates, 2012: *At pages 4-5, a section headed "Signaling in Simple Neuronal Circuits" and another headed "Complex Neuronal Circuitry in Relation to Higher Functions" briefly describe simple circuits that provide simple reflex behavior and complex circuits that provide visual perception, respectively. *At pages 365-380, discussions of behavior of the leech occasionally use words like "circuitry" (e.g. page 365) and "circuit", "circuits", or "neural circuits" (e.g. pages 372, 374, 377, and 378). *Chapter 24, at pages 497-527, is titled "Circuits Controlling Reflexes, Respiration, and Coordinated Movements", implying that the various examples it describes can be thought of as circuits; a section on page 525, for example, is titled "Circuitry of the Basal Ganglia", illustrated by Fig. 24.29 with a similar caption. *Chapter 26, at pages 565-588, is titled "Critical Periods in Sensory Systems"; page 566 briefly examines whether circuits controlling complex functions might require continuous interaction with environment, asks about mechanisms that stabilize cortical circuits when development is complete, mentions that visual experience refines neuronal circuits for optimal operation, and also mentions plasticity in other sensory circuits; page 581 notes that, after a critical period, "equivalent sensory exposure does not produce an equivalent change in brain circuitry." *A section titled "Neuronal Transplants" on pages 609-610 mentions at page 610 how surviving neurons can reconstitute functional circuits, asserts at page 610 that transplanted cells can be incorporated into synaptic circuitry of an adult host, and shows, in Fig. 27.23 on page 610, reconstruction of cerebellar circuits. Svitkina, T., Lin, W.-H., Webb, D.J., Yasuda, R., Wayman, G.A., Van Aelst, L., and Soderling, S.H., "Regulation of the Postsynaptic Cytoskeleton: Roles in Development, Plasticity, and Disorders", The Journal of Neuroscience, Vol. 30, No. 45, 10 November 2010, pp. 14937-14942, begin their introduction on page 14937 as follows: "The capacity of neurons to function within neuronal circuits underlies all our behaviors, thoughts, emotions, and memories." Yuste, R., "Circuit neuroscience: the road ahead", Frontiers in Neuroscience, Vol. 2, Issue 1, July 2008, pp. 6-9, discusses challenges in the study of neural circuits: *Page 6 refers to the mission statement of Frontiers in Neural Circuits for a definition of "Circuit Neuroscience" as "the understanding of the computational function of neural circuits, linking this function with the circuit micro-structure." *Pages 6-8 discuss four problems that need to be solved to decipher the "transfer function" of unknown biological circuits: Cell types problem; circuit connectivity problem; circuit algorithm problem; and circuit dynamics problem. *Page 8 discusses four methodological technical challenges: Monitoring activity of neuronal ensembles; manipulating neuronal activity, visualizing synaptic connections, and computational and theoretical methods. *Page 9 discusses sociological problems in the publication culture. Neuroscience Publications That Avoid the Term "Neural Circuit" (in alphabetical order by first author's last name) Sanes, D.H., Reh, T.A., and Harris, W.A., Development of the Nervous System, 3rd Ed., Burlington, Mass.: Elsevier/Academic Press, 2012; compared with Squire et al., below, this book is less comprehensive, and very rarely uses terms like "neural circuit". One exception has been found: *Pages 290-291, in a section titled "More Complex Behavior is Assembled from the Integration of Simple Circuits", begins by discussing certain circuits such as in embryonic leeches, and then describes Coghill's investigating how neural circuits develop to generate behavior. Squire, L.R., Berg, D., Bloom, F.E., du Lac, S., Ghosh, A., and Spitzer, N.C., Eds., Fundamental Neuroscience, Third Edition, Burlington, Mass.: Academic/Elsevier, 2008; several chapters of this comprehensive neuroscience textbook use terms like "path" and "pathway", but terms like "neural circuit" appear rarely. A few examples have been found: *Bloom, F.E., "Fundamentals of Neuroscience", pp. 3-13, describes basic patterns of "neuronal circuitry" at pages 6-7. *Cline, H., Ghosh, A., and Jan, Y.-N., "Dendritic Development", pp. 491-516, mentioning developing neuronal circuits at page 491 and the function of neuronal circuits at page 510. *Knudsen, E.I., "Early Experience and Sensitive Periods", pp. 517-532, describes development of neural circuits at page 517, and introduces four examples of circuits that have been relatively well studied, specifically "the circuits involved in (1) song learning in songbirds, (2) sound localization in owls, (3) binocular representation in the visual cortex, and (4) temperament in rats." *Floeter, M.K. and Mentis, G.Z., "The Spinal and Peripheral Motor System", pp. 677-697, describe central pattern generating circuits at page 679, descending control of spinal circuits at page 693, and plasticity in spinal cord circuits at page 696. Other Scientific Publications (in alphabetical order by first author's last name, then in chronological order within a first author) Borck, G., Molinari, F., Dreier, B., Sanderegger, P., and Colleux, L., "Synaptic Mechanisms Involved in Cognitive Function: Cues from Mental Retardation Genes", in Jones, B.C., and Mormede, P., Eds., Neurobehavioral Genetics: Methods and Applications, Second Edition, Boca Raton, Fla.: CRC Press, 2007, Chapter 28, pp. 435-447, at page 444 argues that cognitive functions "depend on the coordination of extended synaptic circuits. This in turn depends on synaptic plasticity, the capacity of individual synapses to adapt their transmission on demand to fit the preconditions of the entire circuit. Intact mechanisms of synaptic plasticity are thought to be an important prerequisite for the development of these complex and dynamic circuits in the brain that underlie cognitive functions." Cronly-Dillon, J.R., "The Cytoskeleton as a Regulator of Cell Shape, Nerve Growth and Nervous Plasticity", in Cronly-Dillon, J.R., Ed., Vision and Visual Dysfunction, Vol. 11, Development and Plasticity of the Visual System, Boca Raton, Florida: CRC Press, 1991, Chapter 15, pp. 275-313, at page 275 mentions as an objective "to examine how growing or developing nervous elements respond to extraneous and endogenous signals to bring about the changes in neuronal circuitry that occur during development, nerve regeneration and learning" and also refers to current thinking about "how nerve circuits are assembled". Fernando, C., Vasas, V., Szathmary, E., and Husbands, P. "Evolvable Neuronal Paths: A Novel Basis for Information and Search in the Brain". PLoS ONE , Vol., 6, No. 8, August 2011, e23534, pp. 1-24, at page 1, propose that a path of activity through a network of neurons can be treated as a unit of evolution; units of evolution with differential fitness can evolve by natural selection. They then show how a population of paths can be hereditary material in a neuronally implemented genetic algorithm. Defining any algorithm implementing natural selection of paths in a network substrate as a "path evolution algorithm" or "PEA", they argue that PEAs are well suited for implementation by biological neuronal networks with structural plasticity. Koopowitz, H., "Polyclad Neurobiology and the Evolution of Central Nervous Systems", in Anderson, P.A.V., Ed., Evolution of the First Nervous System, 1989, Chapter 22, pp. 315-328, at page 326 mentions "how cells are arranged in circuits" and "complex local circuitry involving complex serial synapses". Mancuso, K., Hauswirth, W.W., Li, Q., Connor, T.B., Kuchenbecker, J.A., Mauck, M.C., Neitz, J., and Neitz, M., "Gene therapy for red-green colour blindness in adult primates", Nature, Vol. 461, 8 October 2009, pp. 784-787: *The abstract, on page 784, explains how adding a third type of cone pigment to dichromatic retinas provided the receptoral basis for trichromatic colour vision, allowing exploration of "the requirements for establishing the neural circuits for a new dimension of colour sensation." *Page 786 proposes that a new dimension of colour vision exploited pre-existing blue-yellow circuitry Mancuso, K., Mauck, M.C., Kuchenbecker, J.A., Neitz, M., and Neitz, J., "Chapter 72: A Multi-State Color Model Revisited: Implications for a Gene Therapy Cure for Red-Green Colorblindness", in Anderson, R.E., LaVail, M.M., and Hollyfield, J.G., Eds., Retinal Degenerative Diseases, Advances in Experimental Medicine and Biology, Vol. 664, 2010, pp. 631-638: *Section 12.3, pages 633-634, describes circuits underlying vision, proposing that a low-probability genetic event by which trichromatic color vision arose in primates produced an immediate advantage "by adapting some pre-existing visual circuit for a new purpose", possibly "the high-acuity spatial vision circuit" or "the pre-existing color vision circuit which compared S vs. L cones to provide blue-yellow color vision." *Section 12.4, pages 634-637, discusses in more detail circuits that might provide blue-yellow color vision, and Fig. 72.1 on page 635 compares circuits for dichromats and trichromats, both in a small bistratified ganglion pathway and a midget ganglion pathway. *Section 12.5, pages 637-638, discusses gene therapy to cure human red-green colorblindness, arguing as follows at page 637: "Because all of the circuitry required for taking advantage of a third cone type is already present in dichromatic individuals, it should be possible to transform an adult dichromat to a trichromat with full red-green color vision through the simple addition of the missing photopigment of the retina." Tau, G.Z., and Peterson, B.S., "Normal Development of Brain Circuits", Neuropsychopharmacology Reviews, Vol. 35, 2010, pp. 147-168: *The abstract, page 147, describes how developmental organization of neural circuits is influenced by genetic predispositions, environmental events, and neuroplastic responses to experiential demand; experiential demand modulates connectivity and communication among neurons, within individual brain regions and circuits, and across neural pathways. *Page 147 also states that "a circuit typically refers to a set of interconnected components that together subserve a specific function. A neural circuit in the brain may be a cluster of neurons that receives electrochemical information that the circuit modifies and transmits to other circuits for further modification. Alternatively, a neural circuit may comprise a network of interconnected brain regions that together integrate vast amounts of information and perform more complicated cognitive and regulatory functions." Page 147 further argues that distributed neural circuits are neither present at birth nor are invariant through life: "The structure and function of neural circuits perpetually changes and evolves from the time of first contact between nerve cells."